As with all things Lotus you cannot be to definitive.
i.e.
you will probably find a unit number stamped on the top of the chassis / sub frame rail that matches the number scratched into the body plate ..... but you may not, even on an original chassis
After around 1967 or 68 Lotus stopped putting engine numbers on the back of the cylinder head and replaced it with with a cylinder head code number ... usually but not always, There is no record of how these codes matched engine numbers that we stamped into the block ... usually
Body numbers which differ from the unit number usually appear as a moulded in dymo tape near the solenoid and may be repeated in marker on the inside of matching panels such as door ... sometimes. There is no record of body numbers versus unit numbers
Working with registration authorities who are not familiar with the variations possible in a 1960's Lotus can sometimes be challenging and requires persistence and maybe innovation.
A "matching numbers" Elan is a myth IMHO as the records don't exist to match up all these numbers in any definitive way and its all to easy to fake any of the numbers if you wanted to. Its just hype from people trying to flog a car at an inflated price for no good reason. In the end if you can market and sell a car for the best price based on this concept then more power to you I guess
cheers
Rohan