Shielding itself is not perfect. Probably enough for the simple circuitry of an analog quartz. But it's not guaranteed. It's a buffer that reduces a wave by a few to a few dozen dB. A EM pulse through even a properly grounded faraday cage will still replicate another smaller wave internally.

Just let me collect my tiny mechanical toys, dammit, don't ask questions.

Oh, I didn't mean to rain on your parade. I love my diver's watches. In a similar vein I love having 200M of water resistance even though I'll never take them any deeper than the bottom of a small swimming pool, lol.

It's OK collecting them but "protection against an EMP" does sound a bit weird as a reason :)