Bmw insurance
I too have insured my bikes with BMW for the last ten years. In that time I have some times two, three or only one Bike - always BMWs, on the policy. The insurance underwriters have been NiG, Allianz and now Equity Red Star.
With the former underwriters I have simply contacted Motorrad insurance and told them of additional bikes I wanted to add to the policy. The criteria applied has been that the policy is priced at the insurance grouping of the higher rated bike and all other, lesser rated bikes included at no cost. In the early days this no cost element even waived administration fees.
I contacted Motorrad insurance in February this year to ask about cover in the Balkans, specifically Bosnia. The nice lady on the telephone assured me that cover was included: all I needed to do was advise Motorrad of the dates of travel nearer the time.
I renewed the policy for my sole bike - r1200gs in April at a cost of £131.24 (£0.01 more than last year). The renewal documents boasted of 'new significant cover benefits' and 'high quality cover to policy holders' now that the underwriters were Equity Red Star. Excellent, I thought. Rang up, as advised, to notify Motorrad of the trip dates to the Balkans, only to be told that only EU countries are covered and Bosnia was specifically declined by Equity Red Star.

Ah well should have asked a more detailed direct question at the time. Write it down to experience and move on.
Forward to today. A test ride on a BMW f800gs at a BMW dealership which was added by Motorrad to my policy for 24 hours at no cost. Great bike, I think I will have this. I contacted Motorrad to add the bike to the policy only to be asked for an additional £132. I was told by another nice lady that they have to carry out a quotation for each additional bike now. I was expecting a £30 or so admin fee but not a complete unannounced change to the additional bike policy. I can't find any where in this year's or the previous 5 years renewal documents any mention of a change of policy in regard to multiple bike ownership. In fact the colourful, flashy policy booklets for each year are unaltered apart from the change of name of the underwriter.
I post this tale only to raise awareness of subtle yet unheralded changes to what I thought was a continuation of benefits from the BMW Motorrad policy.
The lesson? Assume nothing, be specific in your questions and look elsewhere next year.
Alan R