Ecuador: postal tax stamps

Ecuador has many postal tax stamps, the majority of which are overprints on such things as regular postage, revenue stamps and even tobacco stamps. I noticed that Scott has notes that a number of the overprints can be found with the overprint text printed either up or down. There are no minor numbers noted for the up vs. down overprint but it intrigues me to find out if a more specialized catalogue of Ecuador has more detail or indicates scarcity through value differences.

Here is an example on Sc. no. RA8, an example of a revenue stamps overprinted as a postal tax stamp.