Logic in splitting lines in Change Orders created using Item Batch

We set the profile option value EGO_MAX_LINES_PER_CO as 500.

In PIM, using Item batch, we loaded 1980 items for Change Order.

The change done was on only one custom attribute.

Eventually, it split into four change orders with different count of lines: 365, 386, 396, 351. They sum up to 1498 which is lesser than 1980. I presume remaining lines did not need change order as it already had the intended change value. Is this correct?

The user is expecting at least there be 500 lines per change order. What is the logic behind splitting into such less count of lines such as 351 which is lesser than 500 set up as value in profile EGO_MAX_LINES_PER_CO.