In regards to the above question, we will make mention of the verdicts of some of the jurisprudents as under:
According to a well-known view, the jurists say that the duration of breastfeeding is twenty one months. However, some jurists allow breastfeeding for two years and they consider it as recommended. Therefore, there is not any specific difference with the well-known fatwa. Here is a brief explanation:
1. It is recommended to breastfeed a child for two years, if possible.
2. It is recommended to breastfeed a child for twenty one months and it is not appropriate to breastfeed the child for more than two years.
3. The minimum duration of breastfeeding is twenty one months.
As for breastfeeding for more than two years, the fatwa (verdicts) of some jurists are as under:
4. A child should not be breastfed for more than two years, as a measure of precaution.
5. It is permissible to breastfeed a child one or two months more than two years (24 months).
For further information in this regard, see index: "The Solution to the Difference between verse 233 of Sura al-Baqarah and verse 15 of Sura al-Ahqaf, question 6499 (site: 6946).
 - Allamah Hilli, Hasan bin Yusuf, Tabsiratul Mu'allemin fi Ahkaam al-Din, pg. 143, Center for Printing and Publication affiliated to Ministry of Islamic Culture and Guidance, Tehran, 1st edition, 1411 A.H.; Tabrizi (r.a); Jawad, New Religious Inquiries (Istiftaat Jadid), vol.1, pg. 372, question 1661, Qom, 1st edition (date unknown).
 - Such as: Imam Khomeini, Sayyid Rohullah, Tawzih al-Masail, Research and Editor: Qulipoor Gilani, Muslim, pg. 522, issue 2366, Center for Preparation and Publication of Imam Khomeini's Works, Qom, 1st edition, 1426 A.H.; Fazel Lankarani (r.a), Muhammad, Resalah Tawzih al-Masail, pg. 447, issue 1978 (no date), Qom, 114th edition, 1426 A.H.; Subhani, Ja'far, Resalah Tawzih al-Masail, pg. 464, issue 2132, Imam Sadegh Institute, Qom, 3rd edition, 1429 A.H.
 - Such as: Sistani, Imam Khomeini, Tawzih al-Masail (without annotation), researcher and editor: Bani Hashemi Khomeini, Sayyid Muhammad Hussein, vol.2, pg. 512, issue 2491, Islamic Publications Office, Qom, 8th edition, 1424 A.H.
 - Tabrizi (r.a), Jawad, New Religious Inquiries (Istiftaat Jadid), vol.1, pg. 372, question 1661, Qom, first edition.
 - Shubairi Zanjani, Sayyid Musa, Resalah Tawzih al-Masal, pg. 540, issue 2500, Salsabil Publication, Qom, first edition, 1430 A.H.
 - Mohaqiq Helli, Najmuddin Ja'far bin Hasan al-Mukhtasar al-Nafe' fi Fiqh al-Imamiyah, vol.1, pg. 194, Religious Publications Institute, 6th edition, 1418 A.H.