I know this is little dated post, but I found this post very valuable with adding the higher level pets into my server and I did not find this information anywhere else, so just to help the next person looking. I used the copy line on prevous pet and then tweaking the stats to the higher level pet and add the info into the pets table.
Now the trick I discovered is there is a column in the pets table labeled "petpower". If you set "petpower" to '45' you will cause the server to reply with the "can not find the pet <petname> ". The fix for this is to just simply change the "petpower" to 40 or lower and now you can summon the pet with the appropriate spells. I am not completely sure why this is setup this way but I am thinking it is probably a way to test and experiment with different pet settings and allowing the admin to keep the pets in the table to save the data but having a simple switch to disable them and prevent accidental use by the players.
Once I changed this field 'petpower' to 40 or lower the pet was able to be summoned in game.