Each message is listed by message ID. The message IDs reported in the first column of each table are sequential. The first table of client messages contains the 10000 series of messages, the second table contains the 10100 series, and so on. When you reach the Server Messages tables, the server messages will begin a new series of number sequences.
You will notice that each table does not necessarily use all the numbers available in that sequence. For example, the first table only uses message IDs 10000 through 10020. The second table picks up at 10100 and goes through 10110. Leaving a range of numbers open allows for the addition of future messages for each component.