I had trouble understanding the question, but it sounds like you said.
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I have some devices where the old version of my app was installed from the store.
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I built a new version of the app. (No mention of what keystore you used… debug or production)
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I tried to install the app on the devices from step 1 above (no mention of how you did this: adb, other?)
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I couldn’t install on some devices unless I first removed the original copy of the app.
While, I’d say we need more details, this sound normal to me.
If you have tried to install a new build of your app on a device where it exists already, these things can happen:
A. If the builds have different package IDs, you’ll end up with two copies of the app on your device.
B. If the IDs match, but you used a different keystore, you may be forced to delete the existing one first. ADB can do this
adb install -r theApp.apk
However, if you have a mismatch and dates are goofy… or in some other case…
C. In some cases however, you will simply have to delete the original app yourself before trying to re-install.
Having said all that, the real question is…
If you build your app (using the same keystore as was used for the original) and you upload that to the store, will your users have to manually delete their installed app first?
The answer is, “No.” Google Play won’t even let you upload the app if it doesn’t fit the right criteria to allow an easy replace on update.