If I understand Andrew's statement, "this collection will be turned into a small museum", this is a private collection which has not yet been accessioned into the new institution's collections.
IMO, as a new museum, you are not bound to employ the former/private collection's numbering system(s), and I would advise you to employ a standard museum accession numbering system that is simple and works logically for you (such as the 'tripartite').
However, you should retain the objects' original numbers in the record as part of their history. All museum databases I know of have fields to record alternative/historical numbers.
It's perfect to begin assigning new numbers as part of your initial inventory, using temporary tags written in pencil as you work through the collections, as there will likely be adjustments to be made (discovering disassociated parts, unnumbered objects, duplicate numbers, etc.).
That said, had these been objects *already* accessioned into your own museum's collections using the original numbering system, I would not attempt to change the old numbering system and reassign new numbers.
Retain these old numbers -- unless you discover duplicate numbers assigned to different objects. Dupes DO need to be corrected and updated (the problem is more common than you think in old collections!). Sometimes an additional suffix number is appended.
For subsequent new accessions and cataloging, move forward with a new, logical system that works for you.
Regarding physical marking of the collections, if your numbering system is significantly different from that of the original collector, there should be no confusion. I don't think you should attempt to remove original number markings unless these are causing conservation issues.
Many museums (especially our oldest and largest) survive and thrive with multiple historic numbering systems in use within their collections. Thanks to modern coll mgmt systems, these are just as accessible and researchable and integrated as their newly-accessioned fellows.
Good luck with the inventory, and may you make great discoveries,
Batja (certified inventory geek)
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Batja Bell
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