I wasn't involved myself, just talked over lunch to some of the guys on the team. The customers for the software are other businesses, each with a pretty large contract volumne and direct negotiations, which meant there was already a lot of documentation on the actual requirements of the customers. From that a ranking of core requirements was compiled, a ranking of requirements that would need to be fulfilled due to current contracts, as well as a ranking of requirements that would probably be required in the future. I think that was most of the first two months. In addition they probably scouted out options for tech stacks.
With that in hand, the rest of the time was basically spent with UML and Figma. So very large iterative class diagrams and User Journeys -> UI/UX.
I think by far the largest advantage they had is that the project manager and several devs had been with company and the product since the 90s, so there was a lot of institutional knowledge on the product and customers.
However, after writing the post above I asked the lead how things are going, and they actually still aren't feature complete (3 years on). So while it has fully replaced the old product and 90%+ works, extending to some of the features is still very hard.
With that in hand, the rest of the time was basically spent with UML and Figma. So very large iterative class diagrams and User Journeys -> UI/UX.
I think by far the largest advantage they had is that the project manager and several devs had been with company and the product since the 90s, so there was a lot of institutional knowledge on the product and customers.
However, after writing the post above I asked the lead how things are going, and they actually still aren't feature complete (3 years on). So while it has fully replaced the old product and 90%+ works, extending to some of the features is still very hard.