Very interesting Chief Counsel opinion on the use of "performing the duties of pilot in command in [an aircraft] with an authorized instructor on board" (commonly referred to as "supervised solo") to meet solo requirements.
You can't mix and match. All of the solo hours need to be either solo or supervised solo. For the commercial ASEL, for example, you can't do your long commercial cross country with a CFI on board and do the rest of the solo requirements by yourself.
2016 Grannis Interpretation
You can't mix and match. All of the solo hours need to be either solo or supervised solo. For the commercial ASEL, for example, you can't do your long commercial cross country with a CFI on board and do the rest of the solo requirements by yourself.
2016 Grannis Interpretation