When a job is added, it gets a job number. Is there a limit to these numbers? If so, what does 24x7 do when it reaches this limit?

The limit the size of the 32-bit integer number which is about 2 Gig.

: When a job is added, it gets a job number. Is there a limit to these numbers?
: If so, what does 24x7 do when it reaches this limit?

That sounds like a reasonable size, but what does 24x7 do when it reaches that limit? Does it go back and re-use numbers that aren't being used?

: The limit the size of the 32-bit integer number which is about 2 Gig.

It does not provide any overflow protection; it simply keeps incrementing the last used number by one every time a new job is created. As a result of that if you hit the top limit for 32-integer value (positive range) the next number will be a negative number which will most likely "logically" damage the job database. If you wish you can provide such protection yourself. If you plan to create/delete jobs dynamically put some IF logic to your script in order to reset the last used number to some usable and yet valid value. The last used number is stored in the registry. You can check the value from your script before creating a new job.

: That sounds like a reasonable size, but what does 24x7 do when it reaches
: that limit? Does it go back and re-use numbers that aren't being used?