New Play 1's Sound Different ?

Speakers are mechanical so they will take time to wear in, also if in a slightly different position they can sound different.

Run Trueplay if you have an iOS device and don't worry.

Someone will be along shortly with the same advice or totally conflicting 😉

To the best of my knowledge all P1s are sonically identical. No running in is necessary. Room and position can make a big difference. For example you may get more bass effect if a speaker is close to a wall.

You could only meaningfully compare them in identical locations. Even then, subjective audio comparisons are notoriously unreliable,

No running in is necessary. Room and position can make a big difference.
I agree with both statements. As to the latter, your experience is another demonstration of the fact that the heard sound is always the result of a speaker+room interaction, and depends on where in the room the speaker is placed as well.

In theory, speakers should sound the same regardless of their placement after Trueplay tuning, and while I have not done this experiment, one way to demonstrate the limitations of Trueplay is to see how this will not be the case in your set ups.

I have 1 of the 2 new play 1's pared with the older one to create a stereo pair, and have swapped them to see and the older play one always seems to sound the richer of the 2 the same result if I switch my third play 1 aswell?

What about after trueplay tuning?

One test of the old v new ought to be easily set up; close enough to an ideal one, to be useful.
Put the old unit and one new one side by side in a room. Group the two to play the same music, and set the volume controls at the same levels on both. Using the controller, mute one speaker and then the other, back and forth a few times. If there is nothing wrong with the older unit, you should not hear any sound differences on the back and forth switching if you are more than 8-10 feet away from the units. Eq flat and loudness/Trueplay off on both.

Maybe Sonos found that too many people prefer the sound of the old Play1 over that of the Play3 and sometimes even the Play5. The new Play1s may have been tweaked to create more distinction between the different models. (just one possible theory)

I can't see Sonos making that kind of change; it would affect the ability of old and new to properly stereo pair.

After observing the results of some other recent changes I'm not convinced Sonos spends that much time considering potential unintended consequences.

Could the Play 1's be on differemt firmware? (Is that possible?)