about which table and archiving object you are actually talking?
Asking with an example makes it much easier than a general question where a trainer may spend an entire day in a class room training.
If you are talking for example about the order table AUFK then it is just so that SAP did a good job decades ago and built a single table for many processes. But you can only archive the process specific data from this table with the process specific archiving objects.
it is not possible to archive PM orders with the PP_ORDER archiving object.
But there are other tables e.g. the table with the CO items which can be archived technically for its own, or process orientated with several other archiving objects, which archive those items together with the process data.
It is then the consultant who has to work it out together with the project team how they will later access the archived data, whether you are satisfield to analyse CO items and sales orders independent from each other, or if you want to see the CO items together with the sales order.
Knowing the SAP help well is fundamental knowledge for such decisions: Archiving CO Line Items (CO) - Cost Element Accounting (CO-OM-CEL) - SAP Library