From Sonos:

While we don’t recommend downgrading your products to S1 after updating to S2, it is possible to downgrade cross-compatible products by resetting them and adding them to an existing S1 system.

Products that are only compatible with S2 cannot be downgraded to S1. See our article on Sonos S2 compatibility for a list of these products. Note that all settings and preferences, including Sonos Playlists, will be lost when downgrading a product from S2 to S1.

https://support.sonos.com/s/article/4845?language=en_US

The four digits before the serial number on the label on the bottom of the Connect is the year and month of manufacture (Example: 1608 is August 2016). Anything before 2015 is legacy, after 2015 is modern, and 2015 could go either way. Contact Sonos to find out for sure.

This is so frustrating. I have read (for the umpteenth time) the list of compatability and still don’t know what I have because I can’t find Generation anywhere. Is the Series ID: C100 meaningful?

I am sure I don’t have any products that work ONLY on S2. The image I showed you is all I have.

You say you don’t recommend downgrading after upgrading, but what if my system won’t work on  S2?

Can you post a photo of the left half of the label on the bottom of the Connect?

Here are the 2 apps, differences highlighted:

Mod edit: Personally identifiable information removed.

Hi @cranneberry2,

I’ve checked your system and all 4 of your Connects are S2 compatible and are fully upgraded to S2. This means you do not need to use the S1 controller app and can uninstall that as you will only use the S2 app to control your Sonos system from now on.

If you’re having trouble with your music library, I suggest calling our customer care team, as they have more tools at their disposal to help figure out what’s happening with your Music Library. You shouldn’t need to downgrade to S1 to fix any music library issues.

SORRY!  I assumed the info in System Info was complete, and since my Connects are hard to reach, I hadn’t looked at them. Now we know that they were produced in 2017.

Mod Edit: Personally identifiable information removed.

TERRIFIC!

Now I need to find out if the Sonos in my winter house is compatable with S2. I will have someone go in ASAP and take a photo of the bottom of one of the devices. If that system needs S1, will it be OK to have both S1 and S2 installed on my computer and iphone?

How were you able to check my system’s compatability? Did you know the date when you checked or is there another way? I do have a system ID for the winter house here with me now. 

Yes, that will be fine. Just make sure to use the S1 app for your S1 system and the S2 app for your S2 system. 

I checked for any registered devices to your Sonos account and found those 4 Connect units you mentioned in your original post. If you do post any more screenshots or product pictures, please make sure not to include full serial numbers since that could potentially identify your system to others. If you’d like me to check your system at your winter house, you can send me a private message with the details of that system, and I’ll check it out for you 

I will send you a message with a screenshot of the bottom of one of the units as soon as someone can get into the house and take the photo. Thank you so much for your help!