Do AY seat block?
 

Slumming in economy later and hopefully my flight wont be full, so I moved myself from the exit row to half way back in the cabin to an empty row.
Checked the seatmap again later to see how things were going, and the two seats next to were blanked out.
Not sure if that meant I had seatmates even though over half the seats were free, but I moved myself again, doubled checked a little while ago and the same.

So do AY actually block seats (got my BA Gold number in but will change that once i get my bag checked etc.)?

I know BA allegedly do "theoretical seats".

I asked this when I was still AY Gold a year ago. The answer was that it's not an official perk anymore, but they still did it for me at the airport several times. Might be different with AY Plat/BA Gold.

Ah, the eternal question of the mythical seat block. IMO & AFAIK they don't, but still you might find that the only empty seat on the flight happens to be the one next to you. Even in the exit row. :)
BUT you might also find that it's the opposite way - you have a seat neighbour, while there are plenty of other pax without one.

Apparently the flight isn't too full so they mentioned not opening check-in for another hour.
Couldnt be bothered wating so went through PVG security with a mobile BP and no issues. Did think you had to gave a paper one?
My hand baggage may be a tad large but we'll see.

Getting a nice meal in the Air China First lounge. Beats standing around a check in area.

Added: so far, PE looks rammed once again, so wise not blowing a load of Avios on that, or something like £243.
Still people getting on but hopefully I'll luck out. Fingers crossed.

Additional. Sweet. 80% empty in the rear cabin, so a poor man's bed for me tonight :)
Pushed 15mins early although a 14h15? flight time whilst they avoid half the planet.

Not exactly answering the question of blocked seats next to you, but I recently had a all-economy flight with a large group.

When choosing seats we noticed that the front part of the plane was "blocked" for non-status bookings, but when Platinum or Gold card hodlers had a look, there were several free seats and rows in the first 10 rows of the plane. So clearly there is some sort of seat blocking related to status existing.

Was down as OWE on today's HEL-MAN flight.
Chose a window seat.

Got on and 2 seatmates, yet the rows in front and behind are empty.
Either no shows, the passengers chose to sit next to rather than in empty rows (that would have had the same price if they paid) or the definitely no seat blocking there.

I've had several instances where family members/friends have later booked the same flight I am on. When they (non-Plats) are choosing the seat, the seat next to me appears to be taken, even if it appears free for me.

A long time ago there was some news that Finnair had installed a system for "optimal seating" (I think Amadeus Altéa). This is a system that very well can keep track of e.g. platinums and keep seat next to them free as long as possible, among many other airline configurable rules like keeping family members together even when they did not pay for seat selection. So this would correspond to the "theoretical seat" OP mentions for BA.

The very varied experience among platinums at that time showed that either was not all platinums created equal or Finnair had configured it with a set of rules that made this seat block fail on factors incomprihensible to the member. I assume they still use this, but have no idea how well the seat block works IRL today.

I've seen this today with some of the economy "comfort" seats at the front of economy on the A350 (32ABC and 33ABC). In expert flyer they show as available, but with a BA emerald card they are not selectable (interestingly the icon in the web version of the AY seat map picker for these seats doesn't have a person icon, unlike other occupied seats).

Since my BA gold card expired two days ago, I changed the number to my AY sapphire card and now those seats are available to me!

I am not sure what would happen at check in time and whether these "blocked" seats are released, but it was a bit of a surprise that from One World point of view the seats are not available to BA Emerald but are available to AY Sapphire.