I don't believe that large miners operators can afford to just hodl for few months.
The only miner for which we have reliable data is the Australian company DigitalBTC, because it is publicly owned (i.e. its shares are traded on the Australian stock exchange) and therefore they have to publish audited and detailed quarterly reports. They also act as BTC brokers, and are trying to become a software company.
In
their financial report for the second half of 2014 they say
Bitcoins held on 30 June 2014: 3,600
Bitcoins earned from mining: 9,717
Bitcoins sold from mining: (12,559)
Bitcoins purchased for acquisition of mining hardware: 3,165
Bitcoin paid for acquisition of mining hardware: (3,165)
Increase in Liquidity Desk bitcoins: 1,614
Bitcoins held on 31 December 2014: 2,372
Browsing through the exchange "wallets" exposed in
http://www.walletexplorer.com/ we can also find transactions that move largish lumps of BTC from some miners to some exchanges. For example, in
Bitpay's presumed input wallet we find these deposits by KnC
2013-11-18 10:46:54 085b09cfbe1d6f5214842ded9d8d2a50e467a6b51f82fbdaefecc63e7d2b2ebb +2900.00000000 KnCMiner.com
2013-11-23 17:40:08 c61b49f50a6fd7112747375f4cd14cde6e4a2c28d9b88b0ed64b838087fc258d +1000.00000000 KnCMiner.com
2014-01-03 07:20:58 a53e12545d054126d422fdb4f664107843ba5aa2555d9bdb1f759631febb82cd +888.67670000 KnCMiner.com
2014-01-06 15:00:31 fe378b97f1f5dc4dbf3ee6059c6f226988c090eb149a90a66baf0bf5c7a0fb9e +1375.69510000 KnCMiner.com
2014-01-13 10:34:52 fb49859a319462afccea88d50ef0238ada66679ebbb64f172dc5a6dcf57fa41e +849.35700000 KnCMiner.com
2014-01-21 06:29:42 1e89707414df189934e21ef7c200ef7833e2867a062e4084c9a07636d5d0fa3d +497.57430000 KnCMiner.com
2014-01-22 16:06:12 fc0c75776779c48ba4b6fd843848ae7b26ab56263c99aaf0024e4c9056c5a779 +672.85790000 KnCMiner.com
2014-01-27 07:31:57 98435bdcabee4aa43d951f8f4d402fa61ae0006a8388aba49baae3e74af2d8fc +493.60870000 KnCMiner.com
2014-01-27 16:44:32 4570a7a8ae134099def4b6c26c79c8f90b8c754339dafb941ac508835956e1b0 +182.79950000 KnCMiner.com
2014-02-18 08:24:31 a6b640f6b3ccc0a88730797b925a558f25daf8e6390636861583246a810601a3 +4496.11720000 KnCMiner.com
2014-02-20 08:13:24 026f92da78db19fe561a05f0a77104619783452a8f24a4efed8719abd9553a95 +460.31630000 KnCMiner.com
2014-02-24 16:09:50 0621cddd70fb86f74adda088209831516e6ab9384663fd517bc7fbee7a12f30b +1758.82190000 KnCMiner.com
2014-02-27 14:38:24 7396ca676a238a21fb45f0b96d6191053b25daef0e3e56ad2d54c7cd46442479 +1420.45130000 KnCMiner.com
These amounts may be KnC paying their bills and buying equipment. BitPay presumably sold those coins soon afterwards (One can see in that wallet also many large transfers to Bitstamp and Bitfinex.)
These are only samples, that show only that miners like KnC sometimes sell some of their coins; but we cannot tell how much, because only some of their addresses are identified as theirs in that site.