Cases where not all of the tags show up are usually caused by #defines used in the code. If SlickEdit does not know the value of a #define, it will prevent it from being able to tag it correctly.
You need to add this code's macro information to the list of #defines through the dialog under Tools-->Options-->Languages-->Application Languages-->C/C++-->C/C++ Preprocessing.
Click the "New" button to add a define and then enter its value in the opposite pane. If you leave the value blank, SlickEdit will then just ignore the define but will Tag it.
After defining your preprocessing, you will need to rebuild your files so the information in your tag files is updated. If you are not prompted to Tag your Workspace again go to Tools-->Tag Files, choose the tag file that includes the information you are using (ie: your Workspace vtg (tag) file) and click on "Rebuild Tag File". Make sure that you uncheck the "Retag modified files only" option to retag all of these files, and then click on "OK".