If Sarin was present and only 50 odd people died, that suggests an accident not unrestricted use. https://en.wikipedia.org/wiki/Iraqi_chemical_weapons_program#Iran.E2.80.93Iraq_War
When Iraq used mustard, or nerve agents, the casualty tolls were in the thousands not the tens. There is every reason to logically conclude that Syrian Baathist expertise in weapons is similar to that of Iraq at the time. Common sense says that vague reports complimented with profuse hyperbole should be taken with a large grain of salt.
The fact that Syria was incorrectly accused of using chemical weapons in the past is not grasping at straws. They also only entered the chemical weapon agreement in 2013, provisionally, when they turned over at least some of their stockpile. It is indeed possible that they didn't turn over everything, but it is also quite possible that bombings simply ruptured storage units in rebel hands supplied by the Sauds and Qataris. Especially since Syrian regime would be far more likely to deliver chemical weapons via artillery than via bombs.