Hi Felipe
I'm not 100% certain what help you are asking for. I have a couple of suggestions though.
It sounds like you are running an availability check which is giving an available quantity of 17. You can use transaction CO09 to look at what documents have reserved the other stock. There are also buttons in the ME21N transaction that will take you to this information.
After a delivery document has been deleted you will not see any evidence of it's existence in the LIKP and LIPS tables. The only evidence I have ever been able to find sits in the change history tables which are CDHDR and CDPOS. I can't remember the object id at this time but I'll look it up and let you know.
Regards
Robyn