Eurofighter Typhoon: Tranches, Batches, Blocks, PSCs, PSP/SRPs, Drops.

Is someone able to clear up the differences among them?

There’s much confusion regarding Typhoon’s spiral development and I hope you have an answer for the following questions.

How are the new Typhoon Blocks associated to PSCs and SRPs?
What do these so called “Drops” consist of? And are they UK-only?
Is it true that Germany has bought the SRP 4.2 for its Tranche 1 Eurofighters?
Sometimes I’ve read about Block 5A and Block 8A: what does the A stand for?
And are there any Block 8B/9/10…? How many Blocks does the Tranche 2 involve?

I know these are tons of questions but I rely on you (and I’m sorry for my bad English…).