Sorry but I just don't buy this. As fas as I know, there was no collaborative editing in Excel 15-20 years ago (no Office 365). The only way for several people to edit the same Excel file stored on a network drive would have been to a) make a local copy of the file, b) do the modifications and then c) overwrite the file on the network drive. This would have destoryed _all_ modifications that occured to the file between a) and c), and would have resulted in such high rate of errors that the company would have been simply impossible to operate.
EDIT: As many people have pointed out, Excel did suppport collaborative editing at the time.
Excel supported collaborative editing of binary excel files on SMB shares under windows NT, back in the 2000s.
Now, "supported" does not mean it was in any way good idea, or that it resembled how collaborative editing works in things like Google sheets or O365. Conflicts, deadlocks, etc were common - it's even why I built my first Rails app - we were given excel sheet and asked to do data entry on it over network from multiple machines, I didn't trust it despite a demo of it working and built a quick and dirty webapp.
You could do it. Excel worked well with querying SharePoint. To most users it would be no different from just editing a file. You could also do it via samba.
(Source: I built one of those during my school holidays but I didn't get paid and I didn't have the balls to ask for payment)
I never said it was one file. I think every agent had one file for their area (a few hundred houses). Then some excel macros to pull all those files into one mega file, that the backend system dealt with.
There are entire trading stations built in Excel, used by multiple traders of one firm, synchronized via network drives, doing requests to the broker using VBA. I saw that around 2003.
EDIT: As many people have pointed out, Excel did suppport collaborative editing at the time.