I have to say that all of this material (letters, receipts, manuals and other paperwork) which you seem to have retained adds up to an excellent provenance for the machine, so if you (or your descendants) ever eventually decide to sell Micky it would add considerably to the overall value provided it is all carefully kept together.
Maybe print out that page from ETI and add it to the document stash, as a way of saying 'this is how and when the machine was originally ordered'. It's a pity you don't still have that original ETI issue with a hole where the order slip should be.