Here is the the LET explanation of the MB. It's of little help.....

Dear Sir,

Mandatory bulletin L13/116a requires performance of additional checks onto L13 gliders (At this moment, only L13A and L13 reinforced are released into operation, of course subject to meeting of respective regulations).
Positive result of these checks automatically does not mean that glider can be released into operation.
It is just one of EASA requirements for future possibility to fly. Next requirements will follow up and you will be informed continually.
Mandatory bulletin L13/112a remains valid in all points.

With best regards,

Bruno Kovarik
Product Support Department
tel: +420 572 817 665, fax: +420 572 817 669, e-mail:
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Aircraft Industries, a.s., Na Záhonech 1177, 686 04 Kunovice, Czech Republic, www.let.cz