BUG: inconsistency between replace dict using integers and using strings (#20656)
- [x] closes #20656
- [x] tests added / passed
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/21477?src=pr&el=h1) Report
> Merging [#21477](https://codecov.io/gh/pandas-dev/pandas/pull/21477?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/fb6116f35c291ad49702a0e89575a33da37eeaa1?src=pr&el=desc) will **increase** coverage by `<.01%`.
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/21477/graphs/tree.svg?height=150&width=650&token=eZ4WkYLtcO&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/21477?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #21477      +/-   ##
==========================================
+ Coverage   92.07%   92.08%   +<.01%     
==========================================
  Files         169      169              
  Lines       50684    50703      +19     
==========================================
+ Hits        46668    46689      +21     
+ Misses       4016     4014       -2
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.49% <100%> (ø)` | :arrow_up: |
| #single | `42.33% <12.12%> (-0.01%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/21477?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/internals/blocks.py](https://codecov.io/gh/pandas-dev/pandas/pull/21477/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW50ZXJuYWxzL2Jsb2Nrcy5weQ==) | `94.63% <100%> (+0.17%)` | :arrow_up: |
| [pandas/core/internals/managers.py](https://codecov.io/gh/pandas-dev/pandas/pull/21477/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW50ZXJuYWxzL21hbmFnZXJzLnB5) | `96.48% <100%> (+0.01%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/21477?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/21477?src=pr&el=footer). Last update [fb6116f...4729fc5](https://codecov.io/gh/pandas-dev/pandas/pull/21477?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 @peterpanmj : Good start.  Need a `whatsnew` entry in `0.23.2`. @gfyoung : Which subsection under Bug fixes should I add my entry ? @peterpanmj  : `v0.23.2.txt` - `Other` section Wondering am I working in the right direction ? @peterpanmj  yes going in good direction! need to rebase as we moved internals around a bit.  can you rebase Looks like a nice bit of cleanup in Manager.  For Block I wonder if it could share code with Index,
 (Or an object EA?) but that’s a question for another day. thanks @peterpanmj nice patch!