It is probably not a good to idea to upload an item and keep it private for a long time. Seems like Steam will maintain the original upload date for the item's release date. That means by the time you make the item publicly available, the item will already be old and will not appear on top of the most recent items. For customers that look out for new items only, the item will appear out of sight and not many users will take a notice of it.

I've noticed that too... And I was surprised, if possible I'm gonna try to delete my private tracks and reupload them so other can see my projects! If is not considered bad behavior I'll reupload also the 2 that didn't get visibility in the recent list... Let us know if this problem/bug/issue, will be ever solved or is just the way it is... Thanks!

Deleting private tracks should be alright. For the already published tracks, you may try to update the items first. I think that when an item receives an update, it will get on top of the most recent items again, but I am not sure.