HK uses a letter system for date of manufacture. ID means '83, I think.
Older mags might have a numeric date like 9/79.
Not all MP5 mags have a date code. I just got some newly made ones without any date code, just Made in Germany and 9mmx19.
More detail here:
They are the same so long as the design is the same, and are marked as you describe. Cost/value for any German made 30 round curved is the same. Some folks like the LEO markings. The straight mags are not as valuable, and supposedly do not work well with hollowpoints. They work well for me, but I like the curved because they look better! Look out for the 40 round mags, some don't work well, and the Korean mags can be very bad. The POF (Pakistan) mags are apparently good, and a bit less expensive.