I always kept our production Macs (10 of them) up-to-date with the latest software.
I did this all the way through QuarkXPress 8.
When Quark 9 shipped, I only purchased 3 copies but only installed it on 2 machines. From then to today, I may have received two dozen or less files created in it.
After about 6 months of Quark 10 being out, we actually received a file built in it yesterday.
I haven't even bothered to purchase a copy yet, I asked to customer to back-save to version 9.
I will probably break down an purchase one copy of 10, but just one.
On the flip side, I started receiving Adobe CC files just a day or two after it was released.