I can only pick out the production date clearly on this tyre:
This states it was produced in October, 2005, which makes the tyre potentially dangerous and outside of any manufacturer's recommended usage period. The fact that it is cracking up now suggests that the rubber and carbon black compound it is produced from has become unstable and prone to failure. You will also notice that running this tyre as opposed to a new tyre will result in much greater road noise. This is because the rubber compound is now relatively brittle and will not flex or grip as well as it was designed to.
Continue using this tyre at your own risk, but I would recommend a new replacement.
I thought I'd better check the codes on the other tyres. Allways meant to but never got around to it.
There are two shallow lozenge-shaped depressions each side of a "C8FH" moulded into the outside sidewall. One of them seems to be empty, the other contains a very faint alphanumeric code, which I assume is the date stamp. These are, if I'm interpreting them correctly:-
Front OS : JDJ0905 : Week 9, (i.e. Feb) 2005
Front NS : JDJ1005 : Week 10 (ie Feb) 2005
Rear NS : JDJ1105 : Week 11 (ie March) 2005
Rear OS : JDJ1005 : Week 10 (ie Feb) 2005
They are all Bridgstone 175/70R13 SF-226 radials. There are lots of other codes on the tyres but the only one that varies seems to be WK154941-2 (FOS) and WK154941-1 (other three wheels). I've no idea what that means but suspect it might be a mould number.
So they were fitted as a matched set, and are still well within the manufactures advised 10 year lifespan. OTOH, they are outside the 6 year lifespan apparently advised by many car makers.
That seems to be a blanket advisory that has to cover some very heavy and high performance vehicles, which my sub-litre car isn't, especially when driven by me. A lot of the impetus for it seems to have come from Germany, where high speed driving is legal, and some high profile US litigation involving a Ford Explorer rollover.
So I wouldn't personally scrap them on an age basis, but I don't like the look of them much, so I'll probably at least replace the two with the most obvious sidewall fissures.
I'm told part-used tyres are pretty cheap here, (though I dunno where you get them) so I'll look into that.
The spare, which I'd expect to be older, but looks better, is a Chengshin 831 155SR13 (different nominal width and aspect ratio, same rim diameter).
It has an 11-digit code (42707105610) in a shallow lozenge, which seems to be using a different system which I can't interpret at present.
Nearby there's DOT UYE5 HEO427 moulded in relief. Dunno what all that means either, (apart from DOT, probably) but if I had to guess I'd say all the alpha stuff was secret manufacturer jive, and it was made in week 42 of 2007. A youngster!
The last three digits match the first 3 of the numeric code above, so maybe its a mirror, to go with all the smoke?