Are you opening each part, editing, saving, closing. Are you editing parts from assembly? Do you have other files open whilst doing any of this....? If you have multiple files open, it is likely that you actually have more than one instance of some files in memory at the same time - changes to one will not reflect in another instance.
Assembly open also has instances of all constituent parts open 'in the background', drawing of assembly has instances of assembly, and all parts open 'in the background' plus BoM if used.
More detail is needed to understand if what you are seeing is expected behaviour, or indicative of a problem.