False.
In SP of 1.23 as well as 1.24 (which you're apparently talking about as you mention Lori) there are following possibilities:

You shoot a power up:

• If you have no ammo, your ammo gets powered up and you get 20 ammo.
• If you have some non-powered-up ammo, your ammo gets powered up.
• If you have some powered-up ammo, you get 20 ammo.

You use a special move on a power up:

• If you have less than 75 ammo (powered-up or not), you get 25 ammo.
• If you have more than or exactly 75 ammo, your ammo is changed to 99.

These are all possibilities. However, following paradoxes and bugs take place:

• If you have less than 20 non-powered-up ammo, it's more efficient to first shoot all your ammo and then shoot the power up, rather than simply shoot the power up.
• If you shoot a power up while you have more than 79 ammo, your ammo breaks the limit of 99. It goes down to 99 as soon as you touch this type of ammo or destroy this type of power up with a special move.
• A power up most probably (according to experimental research and speculation) is destroyed one frame after collision with a player (who performs a special move). During this frame it can be used once again to get additional ammo, as long as the player is still on a collision position and performing a special move. Buttstomp, unlike other moves, is stopped by collision with power ups, so it can't be used to achieve such advantage, but all other moves (uppercut, sidekick and spinkick) can. Uppercut can be successfully used only in certain conditions though, such as performing it through One Way events below a power up or finding a masking bug allowing standing inside of it. Also, all of these moves occasionally fail.

By the way, all shooting-related facts in this post also apply to TNT power ups (except that they can only be destroyed by TNT ammo).