Engine Control Unit (ECU) Numbers: Meaning & Explanation

Hello,

I bought a used engine control unit (ECU) with a built-in tuning chip to avoid having to solder anything onto the original ECU.
The following numbers are printed on the control unit:
Bosch 0 218 001 619 and 038 906 018.
On my original control unit, the same Bosch number is listed, but the second number is different. It is 038 906 019 A.
Can someone tell me what this second number means, or whether I can install this control unit without any worries? The previous owner (who was also a tuner) told me that only this Bosch number is important!
Best regards,

fred.labosch

PS: MKB is AJM, Passat Variant 85 KW PD.