Glenda I assume you run a Mac? I'm not familiar with Macs, but on my PC plug-ins are still installed under the old version. I don't know if this will work for you (seems to work on PC) but perhaps if you create the same folder structure under the new install and copy the files across you might be able to access them? From memory copying the files across to the new install also works for presets, etc (on PC).
I haven't upgraded to CC2019, but you can see an example below where the old (CC2015) plug-ins are located and where they would be copied for CC2017 (on a PC)...
CC_folders.jpg
With regard to the 'stamp visible' issue I don't have any answer. I have found that it sometimes doesn't work (in CC2017) for some reason, but as it's intermittent I haven't got to the root of the problem (although probably not related here anyway...)
Cheers.
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Note that you would probably only need to copy over the sub-folders that you want to use (ie DFine & Silver Efex)...