Wrinkle Tank Numbering?

[750rickman]

Does anyone have an explanation or understand the numbers stamped in the bottom of wrinkle tanks?
I have attached 3 pictures of the numbers stamped on the bottom of the rear tank mount bracket.

#4.718 - Tank on original frame #4623
#4.821 - Extra wrinkle tank that I have
#4.828 - This was stamped on the tank that recently sold on eBay for $800  - No I didn't buy it!

Should the VIN & Tank number be "close" like the Engine/Frame #s?
Can you guys that have wrinkle tanks and see if they are stamped?
When did HONDA start stamping wrinkle tanks?

Thanks,
Andy

[kp]

4 = 69 The 4 is shortened from 44 being the 44th year of the swearing in of the Japanese emperor 5 (or 45) = 70 You will probably find all wrinkle tanks were made in 1969
8 =  august
21 = day
  KP

[750rickman]

Mystery solved! 
Thanks KP!   

[tomcourtney]

On Honda Monkey bikes from then the tanks and frames were date coded but i have not seen a date code on a 750 frame?