When Baba turned Dharamsee's grapes seedless, did this happen for everyone else who received grapes that day?

No, the miracle of the seedless grapes was a personal experience specifically for Boss Dharamsee, tailored to his state of mind. Chapter 35 clarifies this by including a crucial interaction at the end of the event. While Baba distributed grapes to the entire group, including the devotee Tarkhad, the transformation was unique to Dharamsee's portion. After his amazing experience, Dharamsee asked Tarkhad, "How were your grapes?" Tarkhad replied that his grapes did indeed have seeds. This confirmation, as the text notes, made Dharamsee "extremely surprised in his heart," reinforcing that the miracle was a direct, personal response from Sai to his specific doubts and not a general phenomenon for all present.