do i need to reinstall the wmse2003 update if i do a hard reset?

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No......a ROM Update overwrites your OS.....(which is in ROM).....and therefore is not affected by a Hard Reset.
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It depends. Unfortunately, Dell has made a number of updates that they called a "ROM update" but in fact it is just a patch and doesn't flash the ROM but goes in RAM instead. Those ones should be reinstalled.

Look at the update you downloaded. If it's around 30 MB then it's a real ROM update. If it's much smaller than that then it's just a patch.

where can i check which rom update i have already? I'm not sure if i already have the A05 installed or if its still the A02