Reconstruct when the programme was added
YouTube TV’s recording help says that adding a programme while its episode is already in progress starts the recording at the time it was added. That makes the timing of the Add action important. A hypothetical viewer who discovers a programme twenty minutes after it begins should not assume that selecting the earliest available point reconstructs those first twenty minutes. Keep the episode identity, scheduled airing and approximate time you added it. Those observations explain more than the general statement that the beginning is missing. Adding a programme to Library is a recording instruction, not a guarantee of material already broadcast before that instruction.
Choose the actual playback mode deliberately
For an item being recorded, the publisher distinguishes starting from the beginning, resuming where you paused, watching the currently live programme and, where supported, watching key plays. Check which action you selected. Resume can intentionally reopen a later point; Watch live can intentionally join the current transmission. Neither result establishes the earliest material captured in the recording. Conversely, choosing the beginning of a partial recording cannot make its missing earlier broadcast appear. First separate a chosen playback position from the recording’s actual starting boundary, then compare that boundary with the time the programme was added.
Watch for a later full airing without promising one
Google says a later rerun can replace the partial recording with a full episode if that rerun airs. This is conditional: it is not a published promise that every event will be repeated. Look at the real programme and any subsequent airing rather than set a deadline invented from another series. The recording guidance says current and upcoming airings are added when a programme is selected. Do not remove and re-add it simply to investigate the earlier start; the documented replacement condition is a later full airing, not repeated changes to the Library button. Retain the original episode details while checking for that possibility.
Report a bad capture with the timeline intact
If the recording appears wrong beyond the documented partial-start behavior, YouTube TV says a bad recording can be reported within the video player. Provide the programme, episode or event, airing information, earliest captured point and when it was added. If the full opening was once present and later disappeared, say that explicitly rather than reuse the midway-add explanation. A report should distinguish what was observed from an assumed cause. This is a focused recording question; it does not establish that the home network lost the opening or that changing the television can recover material that was never captured by this recording.
Questions answered
Does adding an episode halfway through guarantee its opening is recorded?
No. YouTube TV says the recording starts from the time you add an episode already in progress.
Can a partial episode later become a full recording?
The current help says a later rerun, if one airs, replaces the partial recording with the full episode.
Sources & further reading
Official references for the subjects discussed. Service terms and device software can change.