How to set up data storage for an online store from different providers?

Question

Data synchronization

There is an online store that operates from the warehouse of ONE supplier (there is no own warehouse).
We take the entire range, prices from him and synchronize 1C reference books every day.
Now we want to introduce an additional nomenclature that the supplier does not have, but should appear in the future.
The question arises of how to properly organize accounting in 1C, so that in the future there would be no doubling of these positions of the nomenclature after the next update of the database.
Example:
Brought to 1C position N - unique id, code 1C.
The supplier has entered position N in his 1C - a unique id, 1C code.
After the database update, there was a duplication of these positions.
Example 2:
Position N was entered in Bitrix - id - missing, code 1C - missing.
The supplier has entered position N in his 1C - a unique id, 1C code.
After updating the database - id and code were manually loaded into Bitrix. Thus - set up synchronization.
But in this case, a lot of manual work. How to get rid of it?
A similar question arises when connecting additional suppliers in the online store.
It will not be possible to establish relationships between products automatically.
It turns out that the product is the same, but the name, id, 1C code and all other "unique" fields are different.
How to set up data storage in 1C from different suppliers so that there is no duplication of goods in the 1C database?
A good example is exist and similar stores.
One product name, while a large number of suppliers with their own inventory accounting systems.