Difference between Langley Hwdc and GBLALA?

[carr0]

Hello,
I am tracking a small parcel I've sent abroad from Britain. The two most recent notices coming up are:

1. Royal Mail. Your package is in transit with the carrier. Item Received by Royal Mail. Langley Hwdc.

followed by

2. Universal Postal Union. Your parcel has arrived at a transit centre, it is on its way. Departure from outward office of exchange. GBLALA.

From what I've read, Langley HWDC is a RM facility at Heathrow, and GBLALA is an outward processing centre, not run by RM but also at Heathrow. Have I understood right? And does the second notice mean the parcel has cleared customs and is on its way to the airline, or does it still have to go through customs first?

Many thanks for any help with this.
Carr

Edit:

I think this must have gone through customs now, because there is a newer item on the tracking which says

3. Royal Mail. Your package is in transit with the carrier. Item Leaving the UK. Langley Hwdc