It will be purely at the discretion of the first airline you use (the flight to SFO.) Most (not all) airlines have interline baggage agreements, so they CAN through-tag your bags to Dublin. However, some airlines have a policy of NOT through-tagging bags when the flights are on separate tickets/reservations. Your best bet is to phone the airline you'd use and ask them what their policy is on through-tagging. You'll probably have to pay their checked bag fee, and you might have to observe their checked bag rules (size, number) which might be more restrictive than Aer Lingus' rules. If your bags are not through-checked, then you need to leave yourselves a lot of time at SFO to make the switch. Report Abuse. JoanneH on Nov 1, 13 at 05:25 PM. Through tagging works best if the airline you fly to SFO on is a member of the same air alliance as Aer Lingus.