Does SS get notified also and does the timeline update?

I did the eform 4 and next week it'll be over 90 days... before that, it took 90 days to get certified initially...

Are you talking about when using EForm 4?  If so, then yes the approval email with the pdf of your stamped Form 4 is sent to both you and your dealer.  

With the one I just got back, SS somehow got notified, because I got an email from them saying it was approved a few hours later, but I strongly suspect they aren’t getting told by the ATF.  The ATF wouldn’t know that SS was involved, plus they aren’t going to send tax information to someone outside of the transferor and transferee.  More likely it’s the dealer updating their SS inventory that lets SS know that it’s approved.

We don't have that ability.

Don’t know what to say.  My dealer and I got the email in the morning, and in the afternoon that same, I also got an email from SS saying it was approved.  I can’t image that the ATF would also send an approved notification to SS (how would they know SS was involved, plus it’s private tax info), so how did they find out?

ATF should be emailing both transferor and transferee a copy of the approved Form 4.
No idea how Silencer Shop knows. At one time SS was using a unique email address for the transferor (dealer) on the Form 4. But I can't find that on any of my eforms.

That'd be how SS knows (assuming they have a "man-in-the-middle" email for every dealer).

This would also require that someone listed the "dealer8456@SS" email on the eForm for notification.

Correct. But that unique email was only on the paper Form 4's. All my Silencer Shop generated eForm 4's have my email address.

I just looked at all my customer orders on my dealer dashboard and none show anything about "stamp received".

People are getting approved?  I’m at day 120ish.

So are 90% of my eForms.