I'm amazed nobody has mentioned how inaccurate SDR receivers are? I have three ranging from 10 quid to about forty quid and they all miss the mark accuracy wise, and while one is always a bit high, the others are random. The SDR software even has an adjustment box so you can adjust things so they read the right frequency. One of mine is over 12.5KHz away from the real frequency, so until I realised, I couldn't understand why some busy frequencies it can hear didn't pop up on my proper radios.
Real radios have amazingly good frequency stability nowadays.
Their ability to tolerate off frequency signals in practice really depends on the receiver bandwidth. Going back a few years to when we channelised in 25KHz steps, we had some problems when 12.5KHz channels started being used. As we are using deviation from a centre frequency for the message carrying system, rather than amplitude modulation, a 12.5KHz radio, with it's reduced deviation just sounds quieter on a 25KHz set up radio. However, the bandwidth usually meant that the 12.5KHz radio, with it's lower deviation , on the next channel up still fell within the pass band, so a radio tuned to 165.100Mhz, heard the radio on 165.1125KHz. On some radios, it was perfectly clean, on others it distorted on loud speech, as the signal crept into the 'too far away' area. On some radios, as soon as the signal went too far away, it simply cut out. Icom amateur sets didn't do this, but their commercial radios had much tighter filtering, and if the signal went outside the pass band, it cut out. The Chinese radios so popular now have frequency steps that even go down to 5KHz, but the filters are quite wide, so they cannot reject strong signals 'next door'. More expensive radios can - which makes them better for professional users, but for amateur users, not just the hams, being able to hear things off frequency isn't always bad.
Most radios now have good enough filtering that a 12.5Khz capable radio can be tuned at the 5 and 6.25KHz steps, one away - up or down, but most cut off anything if they are more than 10KHz away.
SDR receivers have almost no filtering at all, so are very open - add to this their dreadful accuracy and you see issues that are not really there. A repeater on 453.2375MHz locally shows as 453.2382MHz on my frequency counter, but I suspect, based on it's spec, that it is really on 375, and my frequency counter is simply not accurate enough. My best SDR says it is on 453.248MHz, which most people would round up to 250 - a proper legit channel, but it's not!
A proper radio MUST be precise in frequency - there are specifications set down by many worldwide authorities in individual countries, so it makes sense to trust the radio and assume any errors, shifting 5KHz away from the real frequency are NOT coming from the transmitter, but from inaccurate monitoring equipment. If you have local transmitters that you think are accurate - like the coastguard, then see what the SDR reports as their frequency, and then adjust the offset to read the proper frequency - like 156.800MHz. If the coastguard appear to be on 156.807, I would assume this is NOT them, it's you! If I add the offset to my SDRs, next day, that offset will be wrong again, so you can do the calibration on a known frequency to make sure your results are accurate.