By my base, in which all nat/pan models are separated in three main branch like three different brands: "National Panasonic", "National" and "Panasonic", there is no exist the Panasonic RX-7100 and National RX-7100, only National Panasonic brand got the RX-7100 version.
Since that "National Panasonic" is European / Australian / Middle Eastern brand of the matshu **** a company till in the middle of the 80's, perhaps because of some legal limitations (in a some country) had to change the number of that model so that he can sell them.
I noticed that European models of "National Panasonic" and other boomboxes have a 4 band radio scale with FM/LW/MW/SW bands, the Australian bands is FM/SW1/SW2/SW3 or MW and the Middle Eastern models have not FM band until 83'/84' and the bands is SW1/SW2/SW3/MW (while the Panasonic boomboxes for U.S. market more often have only two bands FM / MW).
Also, all the differences which Norm is mentioned is most common in all brands, and these differences are due to the time span (several years) in production, all in relation to improving the quality and adding more convenient options/functions.