since i did read some of mao's writings, the baochun style is one of my favourites due to the philosophy behind them i thought i'll spend some time to chime in on the subject.
plum decorations on pots easily dates back to the 18th century, but this style of plum usage you see here originates from close to 1960s. based on Mao's verses :
of which you can read the line 俏也不争春，只把春来报. beautiful beautiful verse in response to Lv You's writings in song dynasty.
inspired by mao's writing, zhu-kexin created the "bao chun" style since then, and there are many other permutations other than the original shape. yours here is one of the variations known as : 矮梅报春壶 or in short 矮梅壶, short plum pot.
the theme is a little past the ROC period which is why i feel the pot isnt that early and most probably into the CR era already. this sort of 矮梅报春壶 did come in pure 紫泥，pure 清水泥, 内紫外红 is also a trademark of this era. on why i didnt think of it to be hong ni, firstly because of the seal area, where you can see the coarse texture, and a bit "pitted", since large pots are fired with their base often placed down, the pitting is not an artifact from the firing. hong ni is smoother than that, similarly the inside of your pot, i could see small sandy grains (unless my screen is pixelated), that is not very characteristic of hong ni of that time. it could be your white balance but the pot is a bit too red for 清水泥, which is a pretty "ripe" type of clay, would not have the texture as per described. the old 清水泥 was silky and smooth,which ended up being an extremely well loved clay by many famous makers.
the patina is a little glossy, mildly waxy looking, the transition of texture occurs near the mouth the pot. without high resolution photos we can only speculate. early nei-zi-wai-hong had quite good clay selection, so much so that the purple clay is not the darkish purple brown of the 80s, but more towards the color of dicaoqing. later date NZWH has larger contrast.
here's an example of a nice NZWH from the CR era, the cup and the lid inside is NZWH, so you can see the red of the lid vs the "purple clay" of the inside of the cup.... its not too far a color contrast.
and if you go closer to look at the texture of how early NZWH stuff is like its pretty much :
the stamp : 吕益仙 is rather generic.. perhaps this person might not have existed and was a "group" collective name/stamp during CR. maybe there was really such a person but his name doesnt appear to be in current records. if you do a search you might find a chinese post that talks about a pot from the 50s with this name stamp.. but imho the person whom posted on gucn probably got the date wrong since his pot's plum inscription/carving is extremely CR style with white glaze. the other record of 吕益仙 stuff was an 80's pot that was seen on potsart.