Hi Vivian - I consulted with my collections managers colleagues at HAI and they provided these recommendations:
There are two options here. One, would be to use known acquisition dates for some objects and 2024 for objects whose acquisition dates are unknown, with a note that the object was first processed/formally accessioned into the collection in 2024. I would never estimate an acquisition date or use the donor’s death date as that may be inaccurate and can easily become assumed as fact by staff members. You can put estimates in the provenance field though and mark them as such.
The other option, especially if none of the artifacts have even been numbered before, is to just give everything a 2024 number. This gives the collection a clean slate to speak, where you know, institutionally, that the collection was first fully accessioned/processed/inventoried in 2024. Acquisition dates can then be marked in the provenance field.