Now I have needs and based on them hire a developer and  he/she build module or customize odoo.

Over time, new needs have been created and I get help again from a developer but this time a new developer person. My question here is   :   Because of the previous person coded non-standard maybe that  for my new developer customize odoo  has  problem ?

Is this best for me that work with one company or one group to prevent from this problem?