Possibly you just need to ride another 379 km to make that 1000km a even 1000miles. I have 2 sets of pd-a520's that are similar. But were considered the Tiagra series back then. Only cost $35 too. They both took quite awhile to loosen up. But they did loosen up and finally started putting themselves in the position for a easy clip-in.

Looks as if the spindle and construction are pretty much the same. Only yours doesn't require a special tool to remove the spindle. Just a 17mm wrench (spanner?) Though you don't want to re-lube them at this point in time. The main issue currently is partly that the excess grease just hasn't been pushed out of the way. However if you are currently riding in very cold weather. That will keep the lube more viscous too which also will lengthen the break-in period.

Maybe some stick-on lead weights will help!