Yeah, all those P's are confusing but sometimes you get more than you expected. I have a 1972 PR10 which is supposed to be Reynolds butted 531 in the main triangle only. A previous owner had repainted part of it with beige housepaint so I stripped it to bare metal and discovered that everything except the fork was 531 so it's about 85% PX10. Maybe in those bike boom years demand was so high for these bikes that Peugeot used whatever material they had most of; stands to reason that the cheaper models outsold the more expensive ones so their regular hi ten and carbolite tubes may have been in short supply.