Description of the problem

Not really a bug, more of an inconsistent behaviour.
Saving large Raw and Epochs data with split_naming='bids' uses different naming schema.

When I save large Raw, I get suffixes split-01 and split-02, etc. but when saving Epochs, the first split is saved without suffix, while the second one has split-01. See the code snippet below for details. All asserts pass for me.

Is there a reason for such difference?

Steps to reproduce

import mne
from pathlib import Path

sample_data_folder = mne.datasets.sample.data_path()
sample_data_raw_file = sample_data_folder / "MEG" / "sample" / "sample_audvis_raw.fif"
raw = mne.io.read_raw_fif(sample_data_raw_file, verbose=False).crop(tmax=60)
ev = mne.find_events(raw)
epochs = mne.Epochs(raw, ev, tmin=-0.3, tmax=0.7)

raw.save("raw_meg.fif", split_naming="bids", split_size="50MB")
epochs.save("epochs_epo.fif", split_naming="bids", split_size="50MB")

# all these asserts pass
assert not Path("raw_meg.fif").is_file()
assert Path("raw_split-01_meg.fif").is_file()
assert Path("raw_split-02_meg.fif").is_file()

assert Path("epochs_epo.fif").is_file()  # this should fail though
assert Path("epochs_split-01_epo.fif").is_file()
assert not Path("epochs_split-02_epo.fif").is_file()  # this should fail as well

Link to data

No response

Expected results

These two asserts should fail

assert Path("epochs_epo.fif").is_file()
assert not Path("epochs_split-02_epo.fif").is_file()

Actual results

All asserts pass

Additional information

Platform macOS-13.4.1-arm64-arm-64bit
Python 3.11.3 (main, May 15 2023, 18:01:31) [Clang 14.0.6 ]
Executable /Users/dmalt/Applications/miniconda3/envs/mne_cli_tools/bin/python3
CPU arm (8 cores)
Memory Unavailable (requires "psutil" package)
Core
├☑ mne 1.4.2
├☑ numpy 1.25.2 (OpenBLAS 0.3.23.dev with 8 threads)
├☑ scipy 1.9.3
├☑ matplotlib 3.7.2Installed osx event loop hook.
(backend=MacOSX)
├☑ pooch 1.7.0
└☑ jinja2 3.1.2

Numerical (optional)
├☑ sklearn 1.3.0
├☑ pandas 1.5.3
└☐ unavailable numba, nibabel, nilearn, dipy, openmeeg, cupy

Visualization (optional)
└☐ unavailable pyvista, pyvistaqt, ipyvtklink, vtk, qtpy, ipympl, pyqtgraph, mne-qt-browser

Ecosystem (optional)
└☐ unavailable mne-bids, mne-nirs, mne-features, mne-connectivity, mne-icalabel, mne-bids-pipeline