There are lots of thing while dealing with stores, usually whenever a material is received in comapany security will do GIR, GRN goods received note, then stores will inspect the material, whether it is in good condition or not, and then call the indenter,technical person to inspect and once the inspection is done then the date on which goods are inspected that date is taken as date for A/c Also many companies have lots of procedures of their own so they might purchase a machine and not use it for 2 months so after two months the date on which they use it is the date of commissioning.
For simple purpose if you are confused just take the date of invoice as date of receipt for accounts ,,,