For working in "office support" I doubt you can work with older licenses if a user comes to you with a problem on version xxxx.
In my case I sometimes have to look at some special Excel sheets, so the company I do this task for had to install for each possible Office version a VM I can access. Cost: bearable, as only 1 license cost is added for the company every 2 or 3 years (might be done via Enterprize/Universal subscription, I do not care).

For personal usage I use either Office XP or Office97. OfficeXP gave me 2 install licenses which are now in VMs (so can be run on some host systems if I need that version), but 97 can be used by myself on ***any*** computer for my purposes AND (bigger motivation) it is portable, so that I can use it without installation anywhere (nags at start about missing entries in registry, but works fine), while I also carry installation files on same USB stick. It is relatively small and has everything I need in everyday doc handling while it is a speed demon on todays HW.

For automated/logged Outlook bulk mail handling Office2000 IMO was the best, IF THE VM IS WELL CONFIGURED. Gives you nice,well ordered folders of mail sent as well as activeX hooks, but I have not checked/done that recently.

In case I personally need to read and partially comment/change current office files, I use Textmaker/Planmaker combo to read current file and save as old style file or do changes directly in the Textmaker/Planmaker SW from SoftMaker. Others use Libreoffice for such tasks, I prefer xxxxMaker, as they have versions for Android as well. YMMV, but if you own a Android device, load and play a bit. Was reason to ditch free MS Android Office apps for me ;-))

Some newer/last version licenses bought when on sale to be safe if I ***really*** need them, but not even installed, as xxxMaker was good enough and license trouble never materialized. But I am a programmer with a natural aversion to creating overstyled Word documents IAC ;-))

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>Purchasing the recent versions of MS office has become a significant cost. Especially when you are a very limited user of the package now. I very rarely work on office support software to-day. Once in a while every year. How to avoid the trap of Office 365 in such case?
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>You can certainly find legal copies of older versions of MS Office for sale here in Europe. But some are possible not supported any more. I do not care. Not registrable any more, that's of course a no go! What license -, 2010, 2013 - would you buy? Where would you buy it from.
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>That's for use on a plain vanilla Win10 machine.
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>Daniel