If you update from 1.6.4 to 1.7.3 then you need to flash gapps again.
Flashing new build deletes everything in system folder and thats where google apps are. If you have updated any of them before, then updates are in data folder, thats why you still see them, but they usually don't work if the original apk's are missing from system/apps. To get best results (without data wipe), you need to flash the same version of gapps that you had on the previous build. Your gapps will still be up to date because the updates you have installed are in data folder.
Samsung Galaxy Nexus (Stock Android 4.3)
LG Nexus 4 (Stock Android 4.3) x2
Asus Nexus 7 (Stock Android 4.3)
Asus Nexus 7 2013 (Stock Android 4.3)
Asus Nexus 7 4G 2013 (Stock Android 4.3)
Samsung Galaxy Tab 7.7 3G (Stock Android 4.1.2)
Samsung Galaxy Note 8.0 3G (Stock Android 4.1.2)