That's the problem, nobody is going to test the new software unless they have to, it will sit unused until the end of the pilot period as long as the old software is available too. Those people are no cs nerds who like testing new software, they are office people and learning new tools is stressful for (most of) them. I have been there.
I worked in Switzerland for 5 years in the 1980’s before Windows when the IBM PC/AT’s I ordered ran DOS with my own menu software. (And my father who fought in WW2 asked “Didn’t the Swiss allow sealed troop trains through their country?”, but that’s not my topic.) Anyway, I once installed a new version of WordPerfect alongside the old version, guess which version was never used? And the poor secretary who accidentally ran the new version couldn’t work with her old files & went home crying for 3 days. I was blamed for not explaining things, but I was sure anyone could tell the difference between the old & new versions - no, they evidently could not.