I'm *G with SQ. On rare occasions, I've had the FF# not being recognized. Couldn't really narrow it down. Perhaps a typo or a technical glitch at an OTA. It really works most of the time.

In my experience, LH is much better in treating *G than, say, UA. Middle seat blocking in economy works. In J bookings, I can often select good rows (obv, they often block row 1 for their own frequent flyers). And in economy, I often get access to good seats as well (forward cabin or exit row). As long as you don't book Eco Light, of course.

If your BP after OLCI does not show *G, I would suggest dropping by the business class CI counter to have it added. To sum up: Typically, it all works automatically. I get all the *G benefits and frequently, additional-unofficial-soft benefits such as seat-blocking of middle seats or exit row free-of-charge.