I am not sure there is a line to be drawn or if this is even a question to be asked, much less have an answer.........
What Steve Fang has opened discussion to are considerations fraught with dilemma for the individual who wants/needs his bike to look as close to original as possible, possibly under budget constraints and be road worthy as well.
The classic example dilemma for making a bike appear "like original" as follows - To install Yamiya exhaust or to install nos oem Honda 'paragraph' exhaust or seek endlessly for a genuine set of exhaust manfactured the month the owner's bike rolled off the assembly line ?
Yamiya exhaust clearly are not nos, oem parts, they are at best high quality replacement parts, produced to best of my knowledge by a manufacturer of unknown origin.
The Honda 'paragraph' exhaust currently or at least recently available from Honda are clearly nos, but not oem, of a production run well long after 1969.
Specs of production runs of parts are subject to change over the course of time, depending on importing/exporting country requirements, manufaturer and vendor specs.
Obviously when Honda had the 'paragraph' exhaust manufactured, they had emissions and sound compliance laws to conform to.
Hence the paragraph typically seen on the inner aspect of mufflers produced in later years after 1969 was never on the pipes manufactured in 1969.
Nor in recent parts production runs was Honda concerned with reproducing an unstamped muffler with no relief in pipes, much less a muffler with 5mm welded seams and no internal baffling designed to position the early long heavy steel baffles held in by a single not welded in 6 mm bolt.
What Honda was concerned with was producing an exhaust in meeting compliance of current transportation and emissions regulations, not meeting the desirous whim of some exacting restorer's need to fit "Lotus Roots" to his/her early production bike.
And the high quality Yamiya exhaust baffles are different from original Lotus Root baffles, albeit ever so slightly. And the bends in teh exhaust pipes have more distinctive mandrel markings, whereas any Honda pipes do not.
So.......... If we are restoring to "original condition"......... current, recent production nos parts supplied by Honda are not correct for any sandcast, they are not all exactly like the parts manufactured in 1969. (I am willing to bet a replacement oil line manufactured in 1970 and certainly 1971 was not exactly like an oil line fitted to a sandcast assembled at Honda in March or April 1969.) Nor are non-Honda reproduction parts correct for any sandcast for that matter, because they are not nos oem i.e., new original stock, original equipment manufacture.
Another example of the "restored to original" dilemma is date ink stamped side covers......... Does the owner search for the ink date stamped side cover to approximate the month of manufacture for his frame vin ? Or does he just install an original cover and call it good ennough ? Or does he simply buy Yamiya or DSS covers and call it good ? i can tell you, there are those of us out there who could not bear the thought of ink dated stamped side covers, e.g., 43.09.02 on a March 1969 frame vin.
At some point, one is forced to face the subject of compromise.
I imagine any camp within our universe of restorers could argue the correctness of installing later production nos "new original stock" Honda exhaust for a like original restoration. I also imagine we can argue the correctness for installing a set of Yamiyas which are neither nos or oem, but a very good reproduction of the 1969 exhaust. And, we could argue installing new/recent production Honda exhaust as being correct, if one wans their bike fitted only only with authentic Honda factory parts. As well, we could argue for appearance sake the correctness of using hard brittle original brake lines v.s. the good sense and liablity considerations for using current producton nos oem brake lines.
To me, considering original, refurbishing, restoration, replica...........
1. Factory new condition happens one time only, the moment after the bike was rolled off the assembly line, passed final inspection and being readied for partial disassembly to be placed in a shipping crate.
2. Unmolested original conditon is as the bike left the dealer floor, was delivered to the retail customer. Original unmolested condition would have to include possible markings from multiple decades of time and use, i.e., dents, chips, fade, scratches and so on.
3. Restored is restored, no matter attention to finish detail or part appearance correctness. Restored is not the factory new condition nor is restored an unmolested original condition.
4. Replica would be a fac similie thereof, i.e., George Beale RC166 replicas. No original parts are used to create Beale replicas. They are what they are, painstakingly correct replicas within the constraint of sourcing modern materials, etc.
Restored can be to original appearance or it can be to the restorers desire. And, the considerations never end in the futile search to accomplish a conditon of unattainable perfection to "restored like original condition."
Does this mean restored to original condition using only Honda parts......... ? Or restored to correct original appearance using reproduction parts such as Yamiya that are not nos oem........... ? Or using old brittle short neck brake lines for correctness sake vs using nos oem Honda brake line for a road worthy ride ?
Is the bike going to sit and never started after restoration ? Or is the bike going to be placed in active service afer the restoration ?
To me, the choices are clear, what parts i would use depending on what the plan for the bike is after restoration is completed.
I sure as hell don't want an unavailable and irreplaceable brittle short neck brake line to fail in service nor do i want to be pouring the products of combustion through a rare set of Yamiyas.
Ultimately, discussions of this sort have both objective and subjective considerations , sometimes under the constraints of budget and other times the contraints of liablity considering resale.
Making a bike look correct, complete and like original can be crazy making and it seems we sandcast guys certainly like to pay attention to detail, so it could be suggested there is at least a little bit of crazy in every one of us.
Where to draw the line is up to the individual owner. Our work will draw subjective critique of fellow owners and objective study of existing machines and period literature.
The very most important thing is, we have fun doing it and do all we can to build comraderie and fellowship.