All records belonging to the same high-level group share the same ID pool. For example, sales orders and invoices both belong to the group of transaction records. When you create a sales order and it is assigned 1234 as the internal ID, you should not assume that the internal ID of the next sales order will be 1235. If an invoice or another transaction record is created right after sales order 1234, that record might have 1235 as internal ID. Additionally, there can be gaps between internal IDs. Two sales orders created a few minutes’ apart might have a significant gap between their internal IDs.
Attaching the suiteanswer link: Using Internal IDs, External IDs, and References