There is a neat alternative which I like. Again make a plain slide with the
names of all the speakers on it. You can place them in boxes if you wish.

Save each presentation to a folder but [important] save them as .pps files
(PowerPoint Show). Highlight each speaker's name in your master slide and
insert a hyperlink to the PPS file relevant to that speaker.

Now start with the master slide. When you click on the name, the first slide
for that speaker will appear. When they are finished, after the black last
slide, the show will revert to your master, ready for the next speaker. If
your speakers change order, it makes no difference!

Terry