First of all, thank you for your hard work on the pool and for the detailed explanation.
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The bulk of the remaining offline wallet funds are funds held and currently untouchable in the offline wallets from the withholding attack over a year ago which is awaiting legal confirmation before I can distribute it to affected miners from that time period.
Aside from that, as of now for some stats: there are roughly 30 BTC worth of funds as a the sum of all active miners who haven't yet reached the default or their set minimum payout. There is about 1 block worth of payout queue backlog in offline wallet funds. In total if every miner were to be paid their full balance today it would be a total of about 55 BTC.
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1) Did I understand you correctly that all 298 BTC currently residing on the address 18d3HV2bm94UyY4a9DrPfoZ17sXuiDQq2B are not meant for payments for shalved shares of common miners ?
2) According to the numbers above, for the pool to be able to pay for all shelved shares the pool needed extra 25 BTC (55 BTC - 30 BTC) or basically one mined block. Is it correct?
1) Shelved shares don't exist as BTC anywhere. They've never been mined. Actual funds are not anything to do with shelved shares. And again, while unrelated to shelved shares, looking at the balance for cold wallet addresses isn't useful, since these wallets are used for other purposes.
2) The payout queue includes estimates for the current round. So let's say the payout queue is at ~55 BTC. The pool finds a block, 25 BTC is paid, and then estimates for the next round are included again bringing it back to ~55 BTC (+/- depending on who's still at/above minimum payout).