Ok, apparently we are in need of some clarification here. AlSi7Mg and AlSi7MgCu are designations from obsolete specifications like DIN 1725-2. EN 1706 is the superceding document for aluminium foundry alloys. Within this specification there are three "Alloy designations" that fall under the AlSi7Mg "Alloy Group", which can be referenced by a Numerical designation or a Chemical symbol designation:
Numerical Chemical symbols
EN AC-42000 EN AC-AlSi7Mg
EN AC-42100 EN AC-AlSi7Mg0.3
EN AC-42200 EN AC-AlSi7Mg0.6
All three of these alloys contain the same amount of Si-- range is 6.5 to 7.5%. The Cu content is quite different-- alloy 42000 allows for 0.20% Cu in castings (0.15% in the initial ingot), alloys 42100 & 42200 only allow Cu up to 0.05% (0.03% in the ingot). BS1490 alloy LM25 allows for Cu to a maximum of 0.20, which is why I stated that this was the appropriate BS equivalent. The three AlSi7Mg alloys differ considerably in other elements like Fe, Mn, Ni, Zn, Pb, & Sn.
I have no idea about LM200. I can only conclude that your sales people and/or the customer are confused and/or ignorant. I agree that it is a major frustration dealing with people that aren't precise in their material specifications. Quoting AlSi7Mg without appropriate attribution of the industry standard (EN, DIN, etc.) only leads to this type of confusion, and obviates the necessity for many of the details (quality control, mechanical properties, etc.) that these standards require. If you have any further questions, please feel free to post again. Best of luck.