Why can I only upgrade my guns to level VII?

I was told a new game plus allows you to upgrade your guns to level X. But here I am stuck with guns maxed at VII (seven), which is a boost from V from the last playthrough, but I thought the new game + meant I get level X guns.

Why is my upgrade max level VII? I'm at the first part of a new game that lets you upgrade your weapons.

According to this forum thread, you can only upgrade them to level 7 without "finding" them a second time. When you pick them up again you get 3 extra levels, and you can upgrade through a terminal. Collector's Edition and pre-order bonus weapons can only be upgraded at the terminal, whereas DLC weapons need to be picked up again just like main-game weapons.

As noted below, if you miss a gun you can't currently buy it again, so if you want to fully upgrade it without more than two playthroughs you better not miss any!