It is perfectly safe and acceptable to use data of same weight bullet and similar construction from different manufacturers. An example would be using Hornady 115gr jacketed data with Montana Gold 115gr jacketed bullet. Another would be using Lyman Cast lead 115gr data to load you own cast 115gr bullet.
for example starting load for powder A fills the casing 50% full while powder B starting load fills it 75% full, wouldn't you have different seating depths (COL) for each powder so you dont over pressure?
No, not really. Take a look at the load data in your manuals. They list several powders with different "start" charge and "Max" charge for each powder tested, but the OAL is unchanged. They have already done that work for you.
Your plated bullets can be loaded using jacketed data, just use low to mid-range jacketed data found in your manuals.