This is the most crucial clue. In analog recording, "K" often stands for "Kaset" (Turkish for cassette) or a studio series code. The number 40 might indicate a track position, a catalog number (e.g., "Sahin Records Catalog No. 40"), or even a tape speed (4.0 cm/s – though 4.75 cm/s was standard). Alternatively, in some Middle Eastern labeling systems, "K 40" designates a specific pressing plant or batch.
Now, let's break down the keyword itself to understand what it might mean. i--- Harem Bulbulu Sahin K 40