That would depend on factors like the statutory period of limitation regarding intellectual property, what was agreed upon in the contract(s), whether the IP rights were passed down to heirs, an estate or still lie with the original firm, etc.
I had to wrestle with this a couple of years ago. My employer wanted to make alterations to a building (finished in the early 1980ies) they own, including altering its appearance by adding an extra storey on parts of it.
The building had been designed by two architects (who had quite a name then but sank into obscurity later). The original contract from the mid-1970ies basically stated that they both held a copyright on the building’s design, but was formulated a bit vague. The statutory period of limitation was still 30 years (IIRC) away from running out.
One of the architects was still alive, the other had died, but passed on his IP rights to his heirs.
It took us the better part of five years to sort it out.
