I think what Bartman means is that as long as the other person is registered on the system, you can buy your own ticket and one on their behalf. That is exactly right.
Even though i'm a ST holder and already have my ticket, i can buy friends and family tickets online. You just have to allocate it to the correct relevant person:
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If you select a person that is already attending the match, it tells you and won't let you proceed with the purchase:
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Same token, if you try to buy a junior ticket for someone who isn't a junior, it won't let you proceed.
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It's been 1 ticket per person for years now.
Pick all the seats you want to purchase next to each other, then allocate each seat to the person going. Then they sit together. It's not difficult:
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