I assume that you have a Scott catalog since you have these imperfs listed. These are the distinguishing differences if you limit yourself to only these 5 stamps:
409 = Type I (flat plate), watermark 190 (single line)
482 = Type I (flat plate), unwatermarked
532 = Type IV (offset), unwatermarked
533 = Type V (offset), unwatermarked
534A = Type VI (offset), unwatermarked
The Scott catalog illustrates the different types.
The watermark produces thinner paper. Therefore, when held up to a light and looking through the back of the stamp, the watermark will appear "white/light".
Watermarks are typically illustrated as "black" images in the catalog as an aid for the normal method of viewing watermarks with the stamp face down in a black tray using watermark fluid.
If using the "light" method, keep in mind the US watermarks 191 and 190 are often not very well defined (or not always very clear). If you see a watermark on that stamp, it will definitely be watermark 190.
The types IV-VI will ONLY exist unwatermarked for the this stamp. So you don't have to worry about the watermark for those types. But for the Type I you listed...
Watermark 190 is notorious for another reason -- there are a few positions on the pane in which the watermark barely appears at the corner(s) or along one edge. So if you don't see a watermark using the "light bulb" method, it is NOT necessarily unwatermarked. You should use watermark fluid in a black tray to confirm absence of watermark (paying special attention to possible fragments of one of the watermark letters in the corners or along the edge).
On a side note, if you have the Scott US Specialized catalog, there is a ~30 page section in the Introduction called the Identifier of Definitive Issues. It lists all the definitives in order of DESIGN number, and then a short description of some of the identifying characteristics of each Scott number for that design. I've always found it rather useful when I couldn't remember "where else to look" for possible perf/watermark/design/paper... varieties.