Replacing New Construction Windows

[Windows on Washington]

Looks pretty standard to me. Pics are small on the phone.

[HomeSealed]

I would have done that differently, however that doesn't necessarily make it wrong. Unfortunately without knowing what they did under the surface it will be impossible to say.

With that said, if the top of the window is aluminum trim wrapped over j-channel and that is caulked to the siding, I'm not sure where any water running behind the siding will be able to exit.... If its not caulked, and if they integrated the j-channel into the WRB (tucked under house wrap and taped), then the j channel could be acting as the head flashing.
Still not going to find that method listed as a "best practice", but at least it would be offering some protection, similar in concept to a window with integrated j-channel.

[bw1021]

Unfortunately the calling is caulked to the siding. I’m not 100% sure what is underneath but I highly doubt the j channel is tied into the WRB.

[HomeSealed]

I read back through, it sounds like the installers just tried to recreate the original install, but with J channel instead of the window having the integrated J. That does still bring up the points that I mentioned though. The new J channel should be taped and integrated into the WRB, and the top piece of J/trim shouldn't be caulked to the siding.

If the company that you used is reputable with good reviews, etc, I'd express your concerns to them and get their feedback.