I'm assuming it means the item that has such a label will no longer be sold in the cash shops and is only avail to buy with sP? Am I correct in that assumption?

Yep that's exactly right. The item may, or may not, show up again. Retired items often make an appearance during the Black Friday sale (in November, near US Thanksgiving). They may also show up for other special sales or events.

Sometimes they also show up in the Free Shop, when and if they open it.

, thank you. Is the free shop opened infrequently, or are there a time I should keep an eye out?

very infrequently - but it is supposed to open some time very soon. Keep a close eye on news for the next few days.

, thank you! I will!

in case you missed the news, the free shop is currently open :). It will run until 11:59pm on September 14

I was paying close attention as you said! Thank you.

I'm gonna close this though, since I don't need anything else in this avenue, so to speak.