BBC Iplayer - missing episode numbers

[NuxRo]

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Certain BBC Iplayer downloads are missing their episode number from the output filename which is very annoying as then one needs to go and manually check viewing order and rename files.

youtube-dl -v --all-subs --convert-subs srt -o  "%(title)s.%(episode_number)s.%(episode_id)s.%(chapter_id)s.%(ext)s" https://www.bbc.co.uk/iplayer/episode/b09hc65q/peaky-blinders-series-4-3-blackbird
[debug] System config: []
[debug] User config: []
[debug] Custom config: []
[debug] Command-line args: [u'-v', u'--all-subs', u'--convert-subs', u'srt', u'-o', u'%(title)s.%(episode_number)s.%(episode_id)s.%(chapter_id)s.%(ext)s', u'https://www.bbc.co.uk/iplayer/episode/b09hc65q/peaky-blinders-series-4-3-blackbird']
[debug] Encodings: locale UTF-8, fs UTF-8, out UTF-8, pref UTF-8
[debug] youtube-dl version 2017.12.02
[debug] Python version 2.6.6 - Linux-2.6.32-696.10.2.el6.i686-i686-with-centos-6.9-Final
[debug] exe versions: ffmpeg 3.0-static, ffprobe 3.0-static, rtmpdump 2.4
[debug] Proxy map: {}
[bbc.co.uk] b09hc65q: Downloading video page
[bbc.co.uk] b09hc65q: Downloading playlist JSON
[bbc.co.uk] b09jxg11: Downloading media selection XML
[bbc.co.uk] b09jxg11: Downloading m3u8 information
[bbc.co.uk] b09jxg11: Downloading m3u8 information
[bbc.co.uk] b09jxg11: Downloading captions
[bbc.co.uk] b09jxg11: Downloading captions
[bbc.co.uk] b09jxg11: Downloading captions
[bbc.co.uk] b09jxg11: Downloading m3u8 information
[bbc.co.uk] b09jxg11: Downloading m3u8 information
[debug] Default format spec: bestvideo+bestaudio/best
[info] Writing video subtitles to: Peaky Blinders, Series 4, Blackbird.NA.NA.NA.en.ttml
[debug] Invoking downloader on u'https://vod-dash-uk-live.bbcfmt.hs.llnwd.net/usp/auth/vod/piff_abr_full_hd/a7645d-b09jxg11/vf_b09jxg11_569e1301-95c1-45e0-bc5a-319e66ae9f86.ism.hlsv2.ism/dash/'
[dashsegments] Total fragments: 926
[download] Destination: Peaky Blinders, Series 4, Blackbird.NA.NA.NA.fstream-uk-iptv_streaming_concrete_combined_hd_mf_limelight_uk_dash_https-video=5070000.mp4

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Output filenames end up as e.g.
Peaky Blinders, Series 4, Blackbird-b09jxg11
Instead of:
Peaky Blinders, Series 4, Episode 3 (Blackbird-b09jxg11)

I think this is a BBC inconsistency as other episodes are OK, see attached images.
Can anything be done about it?

I've tried to capture that "3" in "3. Blackbird" via various output options, but without luck. All I get is Na.Na.NA.

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