Old vs. new

Most new releases of classic recordings are made from digital files taken from who-knows-what generation of the original master tape. And that master tape is prone to deterioration over time! So I prefer and buy LPs made way-back-when they were first issued! Even if they show some usage wear!

I am against digital downloads and streaming because the provenance cannot be verified - unlike physical media like LPs, CDs and Tape. 

In the old days of vinyl, analogue source tapes were mixed down to a master tape. Duplicates of this master were sent to a pressing plant where the records were manufactured.

Today to reissue an album, a digital file is created from the analogue tape and becomes the new master. But to do this, some digital processing and compression takes place, thus changing some of the characteristics of the analogue signal. This file is used to create both vinyl and CDs, although vinyl which is an analogue medium requires different specs than the digital product.
The new file has the proper specs required by the pressing plant, but the sound is no longer identical to the original master due to digital processing.

The quality of these digital masters are of varying degrees of quality depending on the engineer, producer, and record label.
 
The file is sent to the record plant
where the pressing process is the same as before.

As roberjerman was eluding to, these reissues which are now digital come from old analogue tapes which may have deteriorated, or even been lost. So whatever tapes they can find are used to release the album on new vinyl.
Of course, the quality of these tapes will never equal the original masters from years gone by.

lowrider57

... to reissue an album, a digital file is created from the analogue tape and becomes the new master.

Not necessarily. Some reissues are made from analog tape.