System usually SKIP inspection lot number.
Reason could be when users log on to SAP, they assigned to particular SAP application server. This can be display bottom left screen. The server can change every time you log on, it is determined by SAP load balancing process. BASIS can set up users so they can be assigned to same server every time. The vast majority of SAP system have more than 1 application server. Some have hundreds. Each server typically handles about 250 users.
So application server A might be assigned 5 insp lot numers, server B another 5, Server C another 5. The next number used will be determined by the next number in the application buffer that the user is loggef onto. Once the numbers are provided to the application servers, SAP considers these numbers as 'used'. If a server crashes, any unused number in its buffer are lost. When it starts again, it is assigned 5 new numbers.
So..for insp lot numbers, you may often see skips in number.
Another reason for this behavior is if in the production order you delete the inspection lot then the inspection lot data in QALS is also deleted, accordingly the inspection lot number is lost.
SAP note 989067