"Celestion" is a brand of loudspeaker. Just like "Jensen", "Emienence" and even "Peavey".
They are brands which produces speakers meant for use with guitar amps, amongst other types too.
You will hear models like Vintage 30, Greenback, P10, Scorpion, Black Widow....etc. These are the type of models produced by different brands.
Actually Sub bro, I suspect the older models you have tried before are not new off the shelves, but owner's amps (the LC15R). The EL84 have this tendency of wearing out quite fast, along with the driver ECC83 as well. could be the cause of muddy sound. For the LC15R, depending on usage, the tubes can actually show signs of wear even within 1yr. By 3-5yrs it's reccomended to replace the tubes already for this model. I have fixed a couple of these, and on a fresh set of tubes, the output actually increase as much as 50%. And a vast improvement in tones.