Strange occurence while importing a disc
 

I was importing a customized disc I named 622 with 18 songs into the laptop using the external plextor as I always do. It went through the entire group of 18 songs
in the usual amount of time. All siad "imported" as usual.
However, when I went to check the songs, ( I usually play a few seconds of a few songs at random to satisfy myself), 62201 loaded into the playlist, but when I went to 62209 and 62218, they were listed as unknown and didn't make it to the playlist when hitting enter. Be mindful that I DID name all of these with artists and titles.
I checked where they should have been going, which is the C drive of the laptop, and the kma's were in fact listed in there. So when in doubt, rebuild database, which I did, after that, allsongs titles and artists showed up on the search and loaded and played. I have gone thru this process a number of times before exactly the same way and have never had this happen.
Is there any explanation for this?
Has anyone ever had it happen to them?
Is there a certain number of songs that seems to initiate a need for a rebuild?
Really weird, huh?

do they play off the disk ?

yup

did you try and reimport them under a new book id ?