I guessing that they reformulated it to make one oil work for both for economic reasons. If the air cooled oil specs are tougher due to cooling and lubricating requirements, they could call the oil multipurpose and recommend it for both. The water cooled lube requirements are probably surpassed by the air cooled specs. So, they can save money by using one formulation and packaging. Also makes more shelf space in the store. I use it in all my planes. At 40:1 it doesn't make much difference to me. I don't put enough time on any one engine to worry about carbon. I also have a backup bottle of Walmart oil if needed.